Silica Spheres Research Articles

The broadband and omnidirectional antireflective performance of perovskite solar cells with curved nanostructures

Various shaped nanostructures have been continually used in the antireflection of organic-inorganic hybrid perovskite solar cells. A full understanding of the shape-dependent light trapping behavior is the basis for finding the excellent broadband and omnidirectional photovoltaic performance. Hence, three-dimensional models of silica sphere, hemisphere, moth-eye and cone nanostructured perovskite solar cells were performed at omnidirectional angle in this work. We proposed electric field intensity per volume as a key parameter, verifying the transition of light trapping modes of several curved nanostructures from normal incidence to oblique incidence. As the incident angle increases, the antireflection effect of four curved structures becomes increasingly crucial, and the differences among them are also greater. Consequently, the moth-eye nanostructured perovskite solar cell has achieved the best photovoltaic performance considering omnidirectional incidence. The short-circuit current density is increased by 8.4% at normal incidence and increased by 36.4% at 60° incidence compared to the planar reference. Our work offers the theoretical analysis for omnidirectional antireflection structure optimization, and provides guidance for the experimental research and production of potential antireflection structures of solar cell.

PVP-stabilized platinum nanoparticles supported on modified silica spheres as efficient catalysts for hydrogen generation from hydrolysis of ammonia borane

Ammonia borane (AB) is considered to be a promising solid hydrogen carrier. In this work, poly(N-vinyl-2-pyrrolidone) (PVP)-protected platinum nanoparticles are supported on γ-methacryloxypropyltrimethoxysilane (γ-MPS) modified silica spheres (Pt-PVP/SiO2(M)), which are firstly used as highly efficient catalysts for hydrolysis of AB. Platinum nanoparticles possess a tiny size of 2–3 nm and are uniformly dispersed over modified silica spheres. Pt-PVP/SiO2(M) catalysts with a Pt loading amount of 1.30 wt% show the highest catalytic activity with a turnover frequency (TOF) value of 371 molH2 molPt−1 min−1 (866 molH2 molPt−1 min−1 corrected for the surface atoms) at 25 °C. The activation energy is calculated to be 46.2 kJ/mol. Furthermore, owing to the synergistic effect between the modifier of silica spheres and the capping agent of metal nanoparticles, Pt-PVP/SiO2(M) catalysts have a higher loading amount (8.7 and 6.5 times) and TOF value (4.8 and 5.5 times) than the counterparts prepared without γ-MPS and PVP, respectively.

Preparation and application of chiral silica gel spheres based on L-glutamic

无机介孔硅球因其具有足够的机械强度、热稳定性,以及适应多种流动相的优点,成为高效液相色谱(HPLC)柱填料中使用最广泛和最重要的材料。但在此研究领域中,并未见球形的全无机手性硅胶用作HPLC手性固定相。该文以无机球形介孔硅胶作为研究对象,通过堆砌硅珠法,以硅溶胶为原料,L-谷氨酸(L-Glu)为手性源,在手性环境中制造出脲醛树脂与胶体二氧化硅混合的小球,在550 ℃高温下煅烧除去树脂部分,制备基于L-Glu的无机介孔硅胶球。通过元素分析、红外光谱、扫描电镜、透射电镜和氮气吸附等表征证明这是一种具有规则球形的手性硅胶球,其手性来源于硅胶球自身的骨架和孔结构。将L-Glu手性硅胶球作为固定相制备了HPLC色谱柱,以正己烷-异丙醇(9∶1, v/v)作为流动相,流速为0.1 mL/min,考察了该手性柱对一系列外消旋化合物的拆分性能。实验表明,该手性柱拆分了15种外消旋化合物,其中特罗格尔碱、吡喹酮、3-苄氧基-1,2-丙二醇、1,2-环氧己烷、3-羟基-2-丁酮、2-甲基四氢呋喃-3-酮、异丙基缩水甘油醚达到基线分离;还分离了10种苯系位置异构体,o,m,p-氨基苯酚、o,p-氯苯酚、o,m,p-碘苯胺、o,m,p-甲苯胺、o,m,p-二硝基苯、o,m,p-氯苯胺、o,m,p-硝基苯酚、o,m,p-溴苯胺达到基线分离。实验表明,L-Glu手性硅胶球在手性分离方面具有良好的可行性,与普通硅胶相比不需要进一步修饰就可以有较好的手性分离效果,是一种低成本、制备便捷的手性无机硅胶固定相。

Functional polymethacrylate composite elastomer filled with multilayer graphene and silica particles

In this work, a three-component composite elastomer consisting of poly(di(ethylene glycol)methyl ether methacrylate) (PMEO2MA), 110 nm spherical silica particles and multilayer graphene (MLG) is fabricated and its various functions brought about by the characteristic morphology formed by silica particles and MLG are clarified. The presence of silica particles greatly improved the dispersibility of MLG in PMEO2MA, allowing more MLG to be filled. The relative dielectric constant (ε) of the composite elastomers can be increased by increasing the amount of MLG while suppressing the increase in dielectric loss tangent (tanδ). The thermal conductivity of the composite elastomer peak in the middle of the increase in MLGs when the silica particles are not filled, whereas the silica particle-filled system is able to fill the MLGs up to a higher volume fraction and shows higher thermal conductivity. The dynamic viscoelasticity analysis of the composite elastomers shows that the filling effect of MLG is more remarkable in the composite elastomer containing 40 vol% silica particles. The loss factor of vibration damping is found to be larger in the 40 vol% SiO2 - 2.8 vol% MLG composite elastomer over a wider frequency range than in the non-MLG samples.

Controllable Preparation of Core-Shell Composites and Their Templated Hollow Carbons Based on a Well-Orchestrated Molecular Bridge-Linked Organic-Inorganic Hybrid Interface.

Controlling the interfacial effect is facing challenges because of the weak interactions between the inorganic and the organic materials. We found that the silane coupling agents with -NH2 groups (e.g., KH550) play a key role as a molecular bridge that links an inorganic silica template with an organic precursor (i.e., pyrrole) in the process of constructing a spherical silica core-polypyrrole shell structure. The molecular bridge is also suitable for inorganic core templates with cube or rod shapes for the construction of different core-shell structures. These template core-polymeric shell structures can be transformed into well-defined hollow carbons after carbonization and template removal. The outer diameter, hollow-core size, and carbon shell thickness of hollow carbon materials (e.g., hollow carbon spheres) could be facilely controlled by changing the template size or the pyrrole amount. We believe that our work will provide a guideline for the preparation of well-orchestrated carbon-based composites and their templated hollow carbons.

Can sustainable, monodisperse, spherical silica be produced from biomolecules? A review

Spherical silica is a fundamentally important material with uses across a wide and diverse range of areas. However, the synthetic routes to producing spherical silica—typically Stober processes—are inherently unsustainable and environmentally damaging. Petrochemical surfactants, alcoholic solvents, and ammonium hydroxide, which are commonly used, each have their own associated environmental problems. Demand is growing to find new, more sustainable ways, to synthesise spherical silica. Bioinspired and biomimetic silica, produced using knowledge learned from natural silica production methods such as biomineralisation, is an ever-growing field of research, that provides a possible route to more sustainable industrial silica production. Biomolecules can be used to shape and form spherical silica instead of petrochemical surfactants. Water-based chemistries can be used instead of alcohol solvents and ammonium hydroxide. This review establishes the parallels between the natural silica biomineralisation process and Stober processes and focuses on the physicochemical properties necessary for biomolecules to synthesise spherical silica. Recent biomolecule-based syntheses are highlighted, and an outlook is given on further developments in the field.

Systematic preparation of high‐quality colloidal silica particles by sol–gel synthesis using reagents at low temperature

AbstractWe propose a new approach to obtain monodisperse submicrometer‐sized colloidal silica particles prepared via a modified Stöber synthesis method, leading to high‐quality spherical particles with a narrow size distribution. The novelty of this work consists in setting, previously to the synthesis reaction, the initial temperature of the reagents at low values (6−14°C) in comparison to the constant laboratory room temperature, while fixing other experimental parameters such as humidity and reagent concentrations. A series of samples of monodisperse colloidal silica particles were prepared, with diameters ranging from 600 to 1000 nm and exhibiting quite narrow particle size distributions. According to our results, it was established that the initial temperature of the reagent solutions constitutes a remarkable parameter, affecting the particle size, shape, and monodispersity. This experimental approach even allows the size tunability for the synthesis of large spherical silica particles in a one‐step process. Moreover, in combination with spin‐coating deposition, the proposed technique greatly favors the formation of ordered arrays of monodisperse silica particles over silicon substrates in areas as large as several mm2. This is ideal for thermal insulators, photonic crystals, nanosphere lithography, and other engineering and industrial applications requiring high‐quality extended arrays of monodisperse silica particles.

Anisotropic localized surface plasmon resonance of vanadium dioxide rods in flexible thermochromic film towards multifunctionality

Plasmonic thermochromic films are promising for smart window applications. Hereby, we develop a flexible plasmonic thermochromic film towards multifunctionality. The double-layer film consists of a bottom layer of W/Mg co-doped vanadium dioxide (VO 2 ) rods in a polyurethane acrylate matrix and a top layer of hollow silica spheres (HSSs). Based on the finite-difference time-domain (FDTD) method, we demonstrate for the first time, a transverse and a longitudinal mode of VO 2 localized surface plasmonic resonance (LSPR) in near- and mid-infrared bands, respectively, and only the transverse mode contributes to the solar energy modulation performance. The film shows a luminous transmittance of 46.2%, a solar energy modulation of 10.8%, and a critical transition temperature of 36.9 °C. The HSSs overcoating enhances the surface hydrophilicity and thermal insulation, which give rise to more favored functionalities for windows. • The first identification of anisotropic LSPR on VO 2 rods. • FDTD method proves only transverse mode of LSPR contributes to solar modulation. • Simultaneous improved flexibility, wettability, solar and thermal modulations. • The thermochromic film is promised for multifunctional smart windows.

Active Individual Nanoresonators Optimized for Lasing and Spasing Operation.

Plasmonic nanoresonators consisting of a gold nanorod and a spherical silica core and gold shell, both coated with a gain layer, were optimized to maximize the stimulated emission in the near-field (NF-c-type) and the outcoupling into the far-field (FF-c-type) and to enter into the spasing operation region (NF-c*-type). It was shown that in the case of a moderate dye concentration, the nanorod has more advantages: smaller lasing threshold and larger slope efficiency and larger achieved intensities in the near-field in addition to FF-c-type systems’ smaller gain and outflow threshold, earlier dip-to-peak switching in the spectrum and slightly larger far-field outcoupling efficiency. However, the near-field (far-field) bandwidth is smaller for NF-c-type (FF-c-type) core–shell nanoresonators. In the case of a larger dye concentration (NF-c*-type), although the slope efficiency and near-field intensity remain larger for the nanorod, the core–shell nanoresonator is more advantageous, considering the smaller lasing, outflow, absorption and extinction cross-section thresholds and near-field bandwidth as well as the significantly larger internal and external quantum efficiencies. It was also shown that the strong-coupling of time-competing plasmonic modes accompanies the transition from lasing to spasing occurring, when the extinction cross-section crosses zero. As a result of the most efficient enhancement in the forward direction, the most uniform far-field distribution was achieved.

Effect of Alcohol Chain Length on Formation of Cetyltrimethylammonium Bromide‐templated Mesoporous Silica Layer on Gold Nanorods

This is the first study that elucidates the effect of alcohol alkyl chain length on the formation of mesoporous silica (mSiO2) layers on cetyltrimethylammonium bromide (CTAB)‐stabilized gold nanorods (CGNRs). The growth tendencies of the mSiO2 layers on the CGNRs (CGNR@mSiO2) in various alcohol solvents differed quite substantially from those observed for previously reported spherical silica particles. The formation of the mSiO2 layer was closely related to the interaction between the CTAB bilayer and alcohol.

Production of ε-Fe2O3 Nanoparticles in Matrices Constituted by Closely Packed Silica Spheres

Production of ε-Fe2O3 Nanoparticles in Matrices Constituted by Closely Packed Silica Spheres

Thymol-functionalized hollow mesoporous silica spheres nanoparticles: preparation, characterization and bactericidal activity

Antimicrobial natural products show good antimicrobial activities; however, some of them have unpleasant odor or high volatility that limits their application in food industry. One of solutions is to introduce them in inorganic media. In this study, hollow mesoporous silica sphere (HS) was used to encapsulate natural organic antimicrobial agent thymol, and antimicrobial activity of the resulted antimicrobial agent (HST) was tested. Materials characterization revealed that the thymol was successfully introduced into the cavities of HS, and the inorganic host exhibited a high loading capacity of 1320 mg g−1. In addition, the antibacterial activities were tested by double-fold dilution method, the minimum bactericidal concentrations of HST against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) were decreased compared with that of thymol. Furthermore, scanning electron microscopy observation confirmed that HST indeed showed a notable inhibitory effect against E. coli and S. aureus by disrupting cell membrane structure.

Spherical metal oxides-LAPONITE® sheets interactions: Microstructure, rheology and thixotropy of composite gels

The composite LAPONITE®-spherical metal oxides (L-SMO) gels were characterised and compared with pure LAPONITE® gels in terms of rheology, microstructure, and time-dependent ageing behaviour. Microstructures of the L-SMO gels indicated that the LAPONITE® sheets formed bonds in an upright orientation with the negatively charged alumina and silica spheres via heterogeneous charge attraction. The bonds enhanced the strength of LAPONITE® sheets network and resulted in higher yield stress than pure LAPONITE® gel. The composite L-SMO gels displayed higher yield stress as increasing SMO content while the composite LAPONITE®-silica gel displayed higher yield stress than the LAPONITE®-alumina gel. The microstructure of composite L-SMO gels was time-dependent as reflected by increased yield stress with ageing time. The composite L-SMO gels were less time-dependent than pure LAPONITE® gel possibly due to the interruption of heterogeneous charge attraction between edges of LAPONITE® sheets and SMO particles on the EDL repulsive interaction between LAPONITE® sheets. The presence of SMO particles also shifted the location of yield stress maximum of LAPONITE® gel and caused the LAPONITE® gel less shear thinning.

Organic dyes (acid red, fluorescein, methylene blue) and copper(II) adsorption on amino silica spherical particles with tailored surface hydrophobicity and porosity

Organic dyes are common constituents in wastewater and contribute to accumulation of persistent organic pollutants in the environment. Common dyes are aromatic compounds, bearing a variety of hydrophilic functional groups. Their interaction with solid surfaces can thus involve both van-der-Waals and hydrophobic interactions and electrostatic and/or hydrogen bonding. Aiming to tailor adsorbents with specific capacity for removal of dyes, silica microspheres were synthesized, combining aminopropyl functions as moderators of hydrophilic interaction and bridging aliphatic and aromatic functions as potential moderators of hydrophobic and π-stacking interactions. Two groups of samples were produced: non-porous silica spheres with amino or combined amino and hydrophobic residues; and porous polysilsesquioxane spheres incorporating aminopropyl components and organic bridges in the silica network. The hydrophilicity/hydrophobicity of the samples was studied by the absorption of water and benzene vapors. Bridged fragments, expected to promote the porosity of the samples, as well as hydrophobicity, did not contribute to the latter, because polysilsesquioxanes were bearing large numbers of residual silanol groups. Particles synthesized using tetraethoxysilane were up to 130 nm in size and held 1.6–1.8 mmol/g of amino groups, while, materials prepared from bridged silanes featured particle agglomerates up to 300 nm, 2.2–2.7 mmol/g amino groups content, and specific surface area of 540–620 m2/g. Interaction with Cu2+ was used to probe concentration and surface location of the amino functions, reaching 76–203 mg/g. Adsorption of anionic (acid red 88), neutral (fluorescein) and cationic (methylene blue) dyes was investigated revealing multiple interactions between the sorbent and sorbate. The dye sorption capacity values were 81–262 mg/g for acid red 88, 26–132 mg/g for fluorescein, and 55–146 mg/g for methylene blue. Produced silica microspheres have potential as high performance sorbents for the extraction of copper(II) ions and the dyes, and can act as fluorescent carriers after the dye adsorption.

Versatile Hollow ZSM-5 Nanoreactors Loaded with Tailorable Metal Catalysts for Selective Hydrogenation Reactions.

Zeolites are one of the most commonly used materials in the chemical industry, acting as catalysts or catalyst supports in different applications. Recently, the synthesis and functionalization of hollow zeolites have attracted many research interests, owing to the unique advantages of their hollow morphology. In the development of more sustainable processes, the hollow zeolites are often endowed with additional stability, selectivity, and activity. Herein, we present a stepwise synthetic protocol to prepare a range of complex hollow ZSM-5 catalysts with catalytic nanoparticles. Solid ZSM-5 crystals were first synthesized from Stöber silica spheres. This solid ZSM-5 sample was then loaded with transition metals via the impregnation method. A subsequent hollowing process was carried out in hydrothermal conditions in which hollow ZSM-5 crystals with confined transition metals inside were synthesized. More specifically, after the encapsulation of transition metals inside hollow ZSM-5, two different approaches have been further devised to allow the deposition of noble metals into the interior cavities or onto the exterior surfaces of the hollow ZSM-5. The deposition of Pt on the exterior surface was carried out by mixing the hollow ZSM-5 sample with presynthesized Pt nanoparticles. Loading of Pd in the interior was achieved by the galvanic replacement reaction between the Pd ions and embedded transition metals inside the hollow ZSM-5 sample. The catalytic performance of these reactor-like nanocatalysts has been evaluated with hydrogenation reactions in both liquid and gas phases, and their compositional and structural merits have been illustrated. For the hollow ZSM-5 sample with Pd loaded inside, liquid-phase selective hydrogenation of styrene over 4-vinylbiphenyl has been achieved with the ZSM-5 shell acting as a molecular sieve. The deposition of Pt on the exterior has improved the C2-C4 product yield when tested for the gas-phase CO2 hydrogenation reaction.

Template-directed preparation of three-dimensionally ordered macroporous molecularly imprinted microspheres for selective recognition and separation of quinine from cinchona extract

A kind of novel three-dimensionally ordered macroporous molecularly imprinted microspheres (3DMIMs) had been developed for selective recognition and separation of quinine based on the combination of colloidal crystal templating method and molecular imprinting technique. The 3DMIMs were derived from the spherical silica colloidal crystal involving a four-step templating process including infiltration of imprinted precursors, sealing of polyethylene glycol, initiation polymerization, as well as final removal of the colloidal crystal and imprinting template. The resulted 3DMIMs consisted of a three-dimensional, highly ordered and interconnected macroporous arrays with nanoscale thickness of polymer wall, in which numerous imprinted cavities were obtained. The kinetic and isothermal adsorption behavior of the 3DMIMs were investigated in detail. The results showed the 3DMIMs had a rapider mass transfer process, higher adsorption capacities and recognition specificity toward quinine compared with the traditional bulk imprinted polymers. In addition, the 3DMIMs exhibited obvious high permeability and low backpressure at high flow rate as column packing. Extraction experiments showed that the 3DMIMs could effectively separate quinine and its diastereoisomer, quinidine, directly from crude cinchona bark extract with a satisfactory selectivity and elution recovery.

Extending synchrotron SAXS instrument ranges through addition of a portable, inexpensive USAXS module with vertical rotation axes.

Ultra-SAXS can enhance the capabilities of existing synchrotron SAXS/WAXS beamlines. A compact ultra-SAXS module has been developed, which extends the measurable q-range with 0.0015 ≤ q (nm-1) ≤ 0.2, allowing structural dimensions in the range 30 ≤ D (nm) ≤ 4000 to be probed in addition to the range covered by a high-end SAXS/WAXS instrument. By shifting the module components in and out on their respective motor stages, SAXS/WAXS measurements can be easily and rapidly interleaved with USAXS measurements. The use of vertical crystal rotation axes (horizontal diffraction) greatly simplifies the construction, at minimal cost to efficiency. In this paper, the design considerations, realization and synchrotron findings are presented. Measurements of silica spheres, an alumina membrane, and a porous carbon catalyst are provided as application examples.

Biomimetic spherical silica production using phosphatidylcholine and soy lecithin

Spherical silica particles are traditionally made via Stöber and modified-Stöber processes, which commonly use environmental toxins as reagents. Here we report a process to synthesise spherical silica particles using environmentally friendly biomolecules (phosphatidylcholine and soy lecithin) and employing water and soybean oil as solvents, rather than potentially harmful organic solvents. This scalable method represents an important step towards sustainable industrial silica syntheses. Under mildly acidic conditions phosphatidylcholine and soy lecithin can control the condensation of sodium silicate to form discrete, spherical silica particles. Silica particles with diameters ranging between 329 and 2232 nm were readily produced using phosphatidylcholine as the templating agent and soybean oil as the solvent in the presence of sodium silicate. Narrower size distributions (262–1272 nm) were achieved using soy lecithin as the templating agent in an aqueous acetate buffer solution containing sodium silicate. Silica particles grown using low concentrations of phosphatidylcholine and soy lecithin as templating agents formed by a combination of coalescence and Ostwald ripening, whilst particles grown at high concentrations predominantly formed through Ostwald ripening behaviour. The possibility of sustainably producing spherical silica particles in a simple biomolecule-templated synthesis is shown.

Elevated surface plasmon resonance sensing sensitivity of Au-covered silica sphere monolayer prepared by Langmuir–Blodgett coating

The colloidal Langmuir–Blodgett coating process is used to fabricate Au-covered silica sphere monolayer (Au film over silica nanosphere (AuFON)) and study the effects of silica diameter on surface plasmon resonance (SPR) sensing sensitivity. The resulting hexagonal close-packed (HCP) monolayers are prepared with silica sphere diameters of 200, 400, 700, and 1000 nm. In SPR sensing applications, the optical properties of Au-covered silica sphere monolayer are evaluated by measuring normal-incidence reflection spectra and sensing tests. The high sensitivity (nm/RIU) is observed in silica sphere diameter (1000 > 700 > 400 > 200 nm) and plasmon mode (dipole > Fano resonance (FR) > and high order) while the highest sensitivity is 968 nm/RIU (dipole mode, 1000 nm of silica sphere diameter). 3-D Finite Difference Time Domain (FDTD) simulation shows a sensitivity trend similar to the experimental results.

Fourier Transform Infrared Imaging Analysis of Interactions Between Polypropylene Grafted with Maleic Anhydride and Silica Spheres Using Two-Trace Two-Dimensional Correlation Mapping.

A technique for analyzing infrared imaging data based on two-trace two-dimensional (2T2D) correlation analysis is presented to extract pertinent information underlying spectroscopic imaging data. In 2T2D correlation mapping, each spectrum in hyperspectral data is individually compared with a reference spectrum to generate 2T2D asynchronous correlation intensity at the x- and y-coordinates on a 2T2D correlation map. Asynchronous correlation intensity develops only when the signal contribution from a certain species becomes even more significant in the sample spectrum compared with the reference spectrum. This feature can be advantageously utilized to examine molecular interaction or an intermediate form of the component present in a system of interest. 2T2D correlation mapping is examined using Fourier transform infrared imaging data of polymer composites based on polypropylene grafted with maleic anhydride melt-mixed with silica spheres. Infrared images derived by using conventional visualization based on a single wavenumber (i.e., 1713 cm-1) are dominated with the overwhelming infrared absorbance induced by the normal maleic anhydride species, making the identification of subtle but pertinent changes in the composite system difficult. A 2T2D correlation map derived from the maleic anhydride/silica spheres composite developed a significant asynchronous correlation intensity between the infrared bands at 1695 and 1713 cm-1 around a specific region on the map where the maleic anhydride and silica spheres coexist. On the other hand, such a correlation pattern becomes less acute when the silica spheres is modified with the octadecyldimethyl group to prevent the hydrogen bonding with the maleic anhydride. It thus revealed that the silanol groups on the surface of the silica spheres substantially interact with the maleic anhydride via the development of the hydrogen bonding.